Aerosol particles, solid or liquid particles suspended in the air, can affect Earth’s climate by scattering and absorbing sunlight. PM_2.5, particles less than 2.5 micrometers in diameter, are largely responsible for degraded visibility and easily traverse respiratory system pathways causing adverse health effects in humans. Often, a majority of PM_2.5 is composed of organic matter formed through photo-chemical reactions of hundreds of volatile organic compounds (VOC). This process depends on nitrogen oxide radical (NO_X = NO + NO₂) concentrations in the atmosphere, now predominantly contributed by anthropogenic emissions. NO_X and VOC react to produce organic nitrates, thought to be significant contributors to PM_2.5, but for which measurements are generally lacking. My project involves developing a concrete assessment of the role of organic nitrates as contributors to PM_2.5. I am developing an analytical method to thermally desorb organic nitrates from atmospheric particles collected on filters and promptly decompose them into nitrogen dioxide (NO₂). The resulting NO₂ is measured with a Cavity Attenuated Phase Shift (CAPS) spectroscopy instrument. I am establishing whether there is a direct correlation between the concentration of organic nitrates in PM_2.5 and desorbed NO₂. The goal is to quantify organic nitrates without individually measuring each of the likely hundreds present in the ambient atmosphere. Moreover, the thermal desorption process provides information on the physical properties of organic nitrates, such as effective saturation vapor pressure, needed for air quality computer models to accurately simulate their contribution to PM_2.5. As a result, I will help develop a better understanding of how natural and anthropogenic emissions affect the composition of the atmosphere by allowing assessments of how PM_2.5 levels have changed in response to NO_X emission reductions by the Clean Air Act.

Wintertime air pollutant emission trends are poorly understood in comparison to emission trends in the summer mostly due to a lack of available and analyzed data on precursor air pollutants in the wintertime. This creates uncertainty in current atmospheric chemistry models. “WINTER 2015” was an aircraft research campaign launched in February 2015 that was executed to measure pollutant concentrations in addition to other data. All of which were relevant to the transportation, distribution, and chemical kinetics of pollutants and aerosols across the northeastern United States. The colder temperatures as well as lack of available sunlight have significant effects on chemical kinetics in the atmosphere. In particular, during the daytime, nitrogen oxides tend to produce ozone (O₃), a criteria pollutant regulated by the U.S. EPA, but nitrogen oxides destroy ozone at night. Longer nights, and lower sunlight during the day may mean that nitrogen oxides net destroy ozone for much of the winter. Current air quality models do not accurately simulate the nighttime chemistry of nitrogen oxides. I am examining the wintertime relationship between nitrogen oxides and O₃ using data taken in the WINTER 2015 campaign to gain insights into the extent to which wintertime nitrogen oxide emissions produce or destroy ozone. This information will then improve atmospheric chemistry models that are used to forecast air quality in various regions. It is expected that in the wintertime, the amount of reactive nitrogen oxide is limited relative to hydrocarbons. This nitrogen limited regime would mean that reactive nitrogen oxides have a greater role in the destruction of ozone, than the production of ozone.